Air heater



Jan. 12, 1932.

WITNESS A. H. DAVIS, JR 1,840,835

AIR HEATER 2 Sheeis-Sheet l 7 Filed April 10, 1929 INVENTOR JAMMUM AWJ 6 M woww 7C;- Mam/-51.

Jan. 12, 1932. H g ws, JR 7 1,840,835

' AIR HEATER Filed April 10, 1929 2 Sheets-Sheet 2 :lNVENTOR Patented Jan. 12, 1932 ,der the varying conditions of use of such heat ng apparatus,

when the plant is oration.

UNITED V s r ARCHIBALD H. DAVIS, JR, or p rnnKINs MANUFACTURING IooM PANY,

PORATION or PENNsYLVANIA" Application filed April 10,

turein the gases, corrosion of the metal by the acid-forming or corrosive constituents of the gases will be minimized. Howeve'r,un-

the metal surfaces-may drop below the temperature at which moisture will condense, thus making it possible r .ton isshown m the accompanying drawings,

for corrosion to set in. For example, air preheaters used for power boilers are generally designed to operate at high efficiency operating underhigh loads, and under such conditions the 'metal surfaces'are above the dew pointofthe hot gases. Such heaters are, in effect, oversize when the plant operates at reduced load, so that under these conditions the heat exchanging surfaces are usually at a temperature low enough for condensation to take place.

The corrosion of prior heat exchanging apparatus resulting from such condensation has been a serious problem, largely because the corrosion may be rapid and because of the expense incident totaking v the unit out ofservice and repairing it.

An object of the invention is to provide heat exchanging apparatus withmeans for automatically controlling the operating temperatures of the gas contact surfaces, which means are simple, of rugged and-inexpensive construction, and are fully automatic in op- Another object is to provide air heating apparatus with means for regulating the temperature of the heat exchanging unit by. controlling fiow of airor gas through the unit, which means are actuated by heatinduced movements of the unit, 7 p Still another object is t] provide an apparatus of the type referred to with means for automatically by-passing aportion of; the air PITTSBURGH, rsnnsynvama, AssiejnoR of the gases fro straw- 0F EITTSBURGH, PENNSYLVANIA, A coa- AIR HEATER 1929/ Serial'Ne. 353,967.

or heating gases around the unit in accordance with the'tem'perature of the unit, where by to regulate the temperature of the gas contact surfaces.

An especial object isto provide a tubular heat exchanging apparatus which embodies all the advantages and minimizes vantages of prior tubular heaters, in which the heat exchanging unit comprises inter changeable tubular radiators which are individually removable, which is provided with means associated with the air ducts and actuated byexpansion and contraction of the tubes for maintaining the tubes above the dew point, and-which apparatus is compact,"

efiicient, and ofsimple construction. The preferred embodiment'of the nvenin which Fig, 1- is an end elevation; Fig. 2

is a'plan View and Fig. 3 is a side elevation, v,

heat exchanging unit for controlling the effluent temperatures of the air or of the heating gases. In this manner, theltemperature constituents of the heating gases is substanor eliminated. Ineither case,- the purpose is effected by controlling the tially reduced temperature of the gascontact surfaces-and is so referred to herein;

The invention may be practiced in a variety of ways but in the preferred embodiment its objects are attained by regulating amount of fluid or gaspassing unit is ust suflicientto maintain the gas contact 7 surfaces at a ''-temperature whlch gives the .disadis provided with p or air may be regulated as dey I sired, eitherabove or belo-wthe dew point of from the hot gases.

.ithe" flow of air or other fluid,cor of heating v gases, throughthe apparatus in accordance Withthe temperature ofthe unit so that the through the longitudinal channels the desired result. To this end, it is preferred to provide means to by-pass a portion of the cold air or gas as need be, and preferably the means used for this purpose is actuated by expansive and contractive movements of the unit caused by changes in its temperature. Such movements being caused by and directly related to changes in temperature may be said to control the operation in accordance with temperature, and may, for brevity be termed heat-induced movements.

Having reference to the drawings, the embodiment shown is represented as applied to an air preheater comprising a framework and interchangeable tubular radiator sections which are individually removable from the framework. This heater construction forms the subject of a copending application, Serial No. 336,746, filed by me on February 1, 1929.

The framework is preferably built up from structural sections, and in the form shown the top and bottom are formed of 1 and transverse channels 2 connected by angles 3 bolted thereto at the corners. Vertical side channels 4, across the ends of which are connected plates 5, define end openings, and angles 6 are connected to the forward ends of plates to form flanges. The flanges referred to, together with those formed by the outer legs of channels 1 and 2 may be used for connecting air and gas ducts to the framework.

Tubular heat exchanging units are pref erably used, and tubular radiators of the type disclosed in United States Patent No. 1,320,652 to C. Sonneborn, dated November 4, 1919, are preferred. These radiator units comprise tubes 7 welded at their ends to panshaped headers 8 having an outwardly bent peripheral flange 9. The radiators are mounted in the framework one above an other to give sectional stacks from which the individual units may be laterally withdrawn when necessary, and one stack or a plurality may be used, as described in my aforesaid copending application.

I11 this embodiment, spaced horizontal rail members 10 disposed in two opposed ends of the framework are carried by supporting members 11 and 11a, preferably angles, vertically positioned in each side of the openings defined by the channels 4 and plates 5. The angles 11 and 1166 are disposed with one leg against the web of the channels, the other leg being in the plane of the opening. The units are placed in the framework by insertion. through the openings formed by channels 1, 1 and 4, 4, head- 'ers 8 and flanges 9 slidably engaging rails 10. Short rail sections or bars 12 are disposed vertically between rails 10 at the sides of the headers. When the units have been set ,in position in'the framework they are connected to rails 10 and 12 by vertical and horizontal clamping members 13 which engage adjacent edges of the headers of two contiguous units. These clamps preferably are ofchannel form, the inner surfaces of their legs being tapered outwardly, as seen in Fig. 3, this construction giving a wedging action which provides for tight joints, and expansion of the headers between the rails and the tapered'surfaces of the clamps is permitted. The horizontal clamps are bolted directly to rails 12, and the vertical side clamps are connected to the appropriate rails by bolts passing through both the rail-supporting angles and the rails. The spaces not occupied by the clamps are filled by plates '14 of appropriate shape bolted to the rails, as shown in Fig. 1. This provides a gas tight structure in which the fluids on opposite sides of the tube cannot intermix.

In order to provide for longitudinal movement of the radiators due to expansion of the tubes, the rail supporting members at one end of the apparatus, for example, angles 116:, are bolted to channels 4, those at the other end, angles 11 in this case, being free to move over the web of channel 4 upon expansion or contraction of the units. This provides for differential expansion of framework and units, and all of the heat-induced movement of the unit is effective at one end of the apparatus.

Air to be heated is passed into one of the tubes of a unit from a duct 15, and is caused to flow through the subsequent unit or units by a return 16 connected to the opening at the other end, and the heated air then passes into an extension a of duct 15. This circulation of air through successive units is indicated by arrows, Fig. 3.

In accordance with the invention, means are provided for controlling the temperature of the gas contact surfaces by regulation of the amount of fluid flowing through the apparatus, this being preferably accomplished by by-passing an amount in accordance with need. In the preferred embodiment this means comprises a valve which in the form described is situated between ducts 15 and 15a, the latter then forming an extension of cold air duct 15. In the form shown, the valve comprises a fixed plate 17 and a movable plate 18 slidable thereon. These plates are provided with slots or other openings 19 adapted to be moved into or out of register according to the relative position of the plates, and the amount of air passing through the apparatus thereby regulated. In order to prevent air from passing directly from the inlet of duct 15 into duct 15a when the valve is closed, the end of plate 17 is connected by a diaphragm 20 extending between channels 4 and connected to the front of the units. In order to avoid distortion of the fixed plate and consequent disturbance of valve action,

' above the dew point, and to causeopeningof member is preferably corrugated or otherwise made of an expansible nature, as shown I in Fig. 3.

The valve-actuating mechanism comprises a lever 21 connected pivotally'at its upper end to a fixed support 22 and at its lower end to a stud 23' carried by the movable plate. The lever is connected by a link 24, Fig. 3,

V to the movable end of a unit, so that expansive and contractive movements of the units are conveyed to plate 18, and the resulting move the thermal condition of the apparatus.

This may be accomplished by using a support independent of the apparatus, but in the form shown, the support comprises a tube passing from duct 15 through the apparatus and discharging into'return 16. i The portion of the tube within the apparatus is provided with lagging 25, and cold air flowing through the tube serves to maintain it at constant temperature. In this manner, support 22 is substantially invariant and independent of movement of the apparatus,and the valve will function properly.

Heating fluid, for example flue gas, is passed to the other surface of thetubes from a duct 26, and the cooled fluid is exhausted through a duct 27. These ducts are 'connected to the openings defined by channels 1, 1 and 2, 2. The sideropenings of the ap-' paratus, between channels 1, 1 and 4:, 4 are closed byplates, not shown, or in any other suitable manner, the plates being preferably readily removable for ease ofwithdrawing the units when necessary.

In the use of the apparatus, the valve-actuating mechanis m'is adjusted so that all of the air from duct 15 flows through the apparatus'as long as the gas contact surfaces are the valve when those surfaces have cooled below the temperature at which moisture may condense' from the gases.

duct 15 will pass through the radiators.

.Yhen for any reason, for example reduction "of load on the boiler, the unit cools, the tubes will contract, and this movement willbe "transmitted to the movable plate. When the unit has cooled to a point where moisture Under normal operating conditions, the of the units.

tubes of the unit willbe above the temperature may condense, the plate has beenmoved sufficiently to bringperforations'lQinto register, 1

around the apparatus. by flowing, directly from duct 15 into 15a. This reduct on n the amount of airpassingthrough the tubes reand a portion of theair will be lay-passed duces the cooling effect ofthe air upon the V tubes,and in consequence, the tubes run hotterthan ifthe full air'supply were passing through them. v As the tubes heat or cool, plate 18 is moved accordingly to'regulate'the relative position of the plates and thus to permit more or less air flow through the valve, and it can be adjusted in position so that the tubes are always abovethe, dew point and no chemical corrosion can occur:

. The foregoing description appliesto the use of the control means "for preventing cor-,

rosion. lVherecorrosion is not apt to occur, or where control-'ofeither gas or air temperature above or belowthe gas .dew point is desired, the apparatus. is equally applicable. In thiscase the mechanism may beadjusted in any suitable mannerso asto actuate the valve to pass sulficient air to reachthe desired temperature, or to cool the gases to the tie sired temperature. In either case, this is com trolling the temperature of the gas contact surfaces. The temperature responsive elc. ment described above is in effect the heating surface, and. when that construction is applied to this modified use, it may not in all cases give suitable control, because it operates at a temperature intermediate that of the two gases. For this reason the construction 7 explained above is modified so that the temperature responsive element is situated in one of the gas passages to respond solely to the temperature of that gas instead of bemg responsive to the heating surface temperature.

This construction operates in the same manner as before, and will "be readily understood by those skilled in the artwwithout further illustration or extended description.

. It will also'be understood that instead'of bypassing air, gas may be bypassed, the constructlon and operation of the valve being the same as before. i In this manner tempera w ture control is attainable from either/side insteadv of the simple linkage shown. Also,

in the form shown the number of. radiator units or their disposition'in the apparatus may be varied according toneed; and insome. cases a singleheat exchanging unit may be used, the construction in such cases being modified in a manner clearly understood by competent designers.

I claim:

1. Heating appa a-tus comprising a framework, a tubular heat exchanging unit mounted in said framework for free expansion and contraction at one end, a conduit for supplying cold air to one surface of the tubes, means for applying hot gases to the other surface of the tubes, and a valve in said conduit operatively connected to the movable end of said unit for actuation by movement of the unit, contraction of the unit opening the valve to by-pass air when the temperature of the unit is below a predetermined value.

2. Heating apparatus comprising a framework, a. tubular heat exchanging unit ca 'ri d by the framework, one end of said unit being connected to the framework and the other end being free to move in response to heatinduced movements of the tubes, conduits for passing heating fluid over and removing it from one surface'of the tubes, conduits for supplying a cold fluid to and removing heated fluid from the other surface of the tubes, a connection between the conduit-s supplying one surface, fixed and movable perforated plates in said connection, and mechanism connected to the free end of the unit for moving said movable plate in response to moven'ieut of the unit to bring the perforations into register and pass a portion of the fluid directly through the conduits to maintain the gas contact surfaces at a predetermined temperature.

3. Heating apparatus comprising a framework, a tubular heat exchanging unit carried by the framework, one end of said unit being connected to the framework and the other end being free to move in response to heat-induced movements of the tubes, an intake for passing hot gases over one surface of the tubes, conduits for supplying cold air to and removing heated air from the other surface of the tubes, a connection between the air conduits, fixed and movable perforatec plates in said connection, and mechanism connected to the free end of the unit for moving said. movable plate in response to movement of the unit to bring the perforations into register and pass a portion of the air directly through the conduits when the unit has fallen below a predetermined ten'iperature.

4. Heating apparatus comprising a framework, rails supported in two opposed ends of the framework, a heating unit comprising a plurality of radiators carried by the rails and individually removable from the framework, one end of each of said radiators being connected to the framework and the other end being free to move upon expansion and con traction of the tubes, a duct cornected to the framework for supplying cold airto the tubes of one of the radiators and for removing heated air from a subsequent radiator, a connection between radiators for circulating air through the tubes of successive radiators, a valve in said duct intermediate the cold air inlet and heated air outlet operatively connected to the free end of one of the radiators for actuationby movement thereof, said valve when closed passing all of the air through the unit and being opened when theunit is below a predetermined temperature to pass a portion of the air directly through the duct.

5. Heating apparatus comprising a framework, parallel rails supported in two opposed ends of the framework, a plurality of radiaerally elliptical cross section connected at their ends to headers, saidradiators being removably supported in the framework with the headers slidably mounted between adjacent rails, one of the radiators being connected to the framework and the other end being free to move upon expansion or contraction of the tubes, a return connection between radiators, a duct connected to the framework having a cold air outlet to the tubes of one of the radiators and a heated air inlet from a subsequent radiator, a valve disposed in the duct between said inlet and outlet comprising fixed and movable perforated plates, and operating con nections between t e movable plate and the free end of one of the radiators, contraction of the radiators in cooling to a predetermined temperature moving said plate to bring the perforations into registerand pass a portion ofthe cold air directly through the duct.

6. Heating apparatus comprising a framework, a tubular heat exchanging unit mounted in said framework and having one end fixed and the other end free to move upon expansion and contraction of the unit, a conduit having a cold air outlet to thetubes of portion of the unit andan inlet for heater air from the balance of the unit, a valve disposed in said conduit intermediate said outlet and inlet comprising fixed and movable perforated plates and mechanism associated with the movable plate connected to the free end of the unit, the perforations in the plates being brought into register by contraction of the unit when it is below a predetermined temperature.

4. Heating apparatus comprising a framework, a tubular heat exchanging unit comising removable radiators mounted in said framework, return connection between radiators for circulation of air through the unit, each radiator having one end fixed and the other end free to move upon eX- :,f

pansion and contraction of the unit, a conduit having a cold air outlet to one of the radiators and an inlet for heated air from a subsequent radia t r a valve disposed tors each comprising parallel tubes of gen- -.3

in said conduit intermediate saidoutlet F and inlet comprising fixed and movable perforated plates and actuating linkage connecting said movable plate and the free end of one of the radiators and supported from a fixed member carried by the framework, contraction of the unit when below a predetermined temperature bringing the perforations of said plates into register topass a portion of the cold air directly through the conduit;

8. Heating apparatus comprisinga framework, parallel rails supported in two o-pposed ends of the framework, a plurality of radiators each comprising parallel tubes of generally elliptical cross section connected at their ends to headers, saidradiators being removably supported in the framework with the headers slidably mounted between adj acent rails, one end ofthe radiators being connected to the framework and the other end ARCHIBALD H. DAVIS, J R.

being free to move upon expansion or con traction of the tubes, ducts forsupplying hot gases to and removing them from one surface of the tubes, ducts for supplying cold air to and removing heated air from the other surface of the tubes, a connection between the inlet and outlet ducts of one of said surfaces,

a Valve in said connection comprising fixed and movable perforated plates, and operating connections between the movable plate and the free end of one of the radiators, ex-

aansion and contraction of the radiators moving said plate to bring the perforations into or out of register to regulate the tem-.

perature of the gas contact surfaces.

9. An air heater comprising incombination a framework, a heat exchanging unit mounted in said framework for movement relative thereto in response to temperature changes of the unit, a conduit for supplying air to be heated to one heat exchanging surface of the unit, a' conduitfor supplying heating gases to the other surface of the unit, and means associated with one of said 0011'- duits responsive to said movements of the unit for regulating the amount of fluid flowing from that conduit to the unit to maintain the unit at a temperatureabovethe dew point of water. i Y

10. Heating apparatus comprising in combination a framework, a heat exchanging unit mounted in the framework for movement relative thereto in response to temperature changes of the unit, a conduit for supplying air to be heated to one surface of the unit, a conduit for supplying heating gases to the other surface of the unit, and means associated with one of said conduits actuated by said movements of the unit to bypass a portion of the .fiuid fromthat conduit to maintain the temperature of the gas contact surfaces fof the unit near a predetermined value.

11. Heating apparatus comprising in com-,

bination a framework, a heat exchanging unit mounted in said framework for move- 

